Electric explosion initiator



April 23, 1946. D. D. HUYETT EAL Y I ELECTRIC EXPLOSION INITIATOR FiledApril 16, 1940 WILLIAM EARL FLETCHER T T E V v 5 0 0m 5 w &m M m m ,D NA ATTORNEY Patented Apr. 23, 1946 ELECTRIC EXPLOSION INITIATOR DelawareApplication April 16, 1940, Serial No. 329,962

1 Claim.

This invention relates generally to electric explosion initiators andmore particularly to initiators of this type that are used in mining andunder-water blasting.

Explosive initiators adapted to be used for initiating the explosion ofblasting agents such as black powder, dynamite, and the like, have beenformed from a metal shell or case, one end of the shell being closed bya plug through which,

lead wires pass. The end closure or plug has been made from variousmaterials including sulphur cements, lead, mineral'resins such as pitchor asphalt, rubber, and polyvinyl products or mixtures such as mixedpolymerisates of vinyl chloride and other unsaturated organic compoundssuch as acrylic acid esters, maleic acid esters and vinyl acetate.

The lead wires passing. through the plug have been insulated byimpregnating cotton coverings. More, recently, the lead wires passingthrough a rubber plug have been coated with a plastic which is extrudedon the lead wires.

Although many proposals have been made for closing these explosiveinitiator assemblies, access of atmospheric moisture or water to theinterior of the explosion initiator thus rendering it ineffective, hasnot been entirely precluded.

In accordance with the present invention, there is proposed a novel leadwireand plug assembly for electric explosion initiators, said assemblyhaving greatly improved moisture resistance and being otherwise highlyadvantageous.

An object of the invention is to provide a new lead wire and plugassembly for electric explosion initiators.

Another object of the invention is to provide such an assembly which isunitary and which may be readily produced.

Another object of the invention is to provide such an assembly for theclosure of shells of electric explosion initiators, which shells may beconstructed of either a thermoplastic material or of the conventionalgilding metal.

Still another object of the invention is to pro vide an electricexplosion initiator wherein the insulation for the lead wires, the plugassembly and the shell are all of thermoplastic material, thethermoplastic insulation and the plug being merged together at theirjuncture, and the plug and the shell being merged together at theirjuncture to form a unitary thermoplastic housing.

Other objects of the invention will hereinafter more fully appear.

Non-limiting structures constituting preferred embodiments of myinvention as illustrated in the accompanying drawing form a part of thisspeciflcation in which:

Fig. 1 is a vertical, sectional elevation of an embodiment of the leadwire and plug assembly;

Fig. 2 is a vertical, sectional elevation of a conventional glidingmetal shell type electric explosion initiator having the lead wire andplug assembly of Fig. 1 assembled therein; and

Fig. 3-is a similar section of a plastic shell type electric explosioninitiator having the lead wire and plug assembly of Fig. l therein.

Wehave discovered that the objects of our invention may be attained andthat a novel lead wire and plug assembly which precludes the entry ofatmospheric moisture and water to the interior;

of an electric explosion initiator may be produced by employing a plugof thermoplastic material and lead wires coated with a thermoplasticinsulating material, the thermoplastic insulation of the lead wires andthe thermoplastic plug being merged together at their juncture, Bymerged we mean that the contiguous, juncture surfaces unite to form ahomogeneous mass. This type of merging of surfaces to form a homogeneousmass is to be sharply distinguished from a merging of surfaces whereby adistinct cleavage surface between the joined surfaces is produced.

This lead wire and plug assembly may thereafter be assembled into theopen end of a detonator shell which may be either the conventionalglidingmetal type, or, preferably, a shell formed of thermoplasticmaterial. Where the shell is formed of thermoplastic material the plugand shell may be merged together. In this latter embodlment a lead wireplug and shell assembly is produced wherein the thermoplastic insulationof the lead wires and the plug are merged togather at their juncture andthe plug and the shell are merged together at their juncture to -form aunitary thermoplastic housing,

An embodiment of the lead wire and plug ass'embly oi the presentinvention is illustrated in Fig. 1 wherein i represents a tapered plugformed of thermoplastic material. This plug is provided with two smallbores 2 and 3, which are drilled or cast into the plug and which may beslightly flared by means of a taper reamer at their lower ends asindicated by 2 and 3'. The two lead wires 8 and 5 are insulated by acoating of plastic designated as 8 and I. The diameter of the leadwireis slightly smaller than the diameter of the bore and the plasticwhich insulates the lead wire is of such a thickness as to give a tightfit for the insulated lead wire in the bore. At their lower ends thelead wires are bared at 4' portion of the plug.

These lead wire portions lying below the plug are then dipped into aliquid which is a solvent for both the thermoplastic insulating materialof the lead wire and the thermoplastic material of the plug. The solventsoftens and tends to dissolve the surface of the insulating materialcontacted by it. These portions of the lead wires are immediatelyremoved from the solvent and drawn upwardly into the plug so that theportion of the insulation so softened lies within the plug as indicatedat H and H in Fig. 1 of the drawing. The residual solvent retained onthis portion of the lead wires will soften the hole-defining portions ofthe plug to such an extent as to render such portions semi-fluid andsealingly adhesive with respect to the material coating the lead wires.The solvent is then dispersed either by evaporation or by absorptioninto the main body of thermoplastic material and the thermoplasticmaterial of the plug lying adjacent bores 2 and 3 and the thermoplasticinsulating material of the lead wires lying within the said bores mergetogether and form a homogeneous mass. Any excess thermoplastic materialon the lead wires forms small fillets in the slightly flared ends 2" and3" of the bores as shown in Figs. 2 and 3 and upon evaporation of thesolvent therefrom these fillets structurally strengthen and secure theinsulated lead wires adjacent the bores of l the plug.

While we have shown the lead wires tobe two separate wires, it is to beunderstood that they may be in the form of a two-conductor cord or cableinsulated with thermoplastic material, in

which case they may be drawn through a single bore in the plug.

The lead wire and plug assemblies of the present invention are unitarystructures which may be assembled with various types of electricexploslon initiators. The plugand insulating material form an effectiveseal from the shell of the explosion initiator tothe termination of theinsulation at the outer end of the lead wires. It can be readily seenthat the lead wire and plug assembly is of particular advantage forassembly with explosion initiators which are to be fired under watersince the lead wires with their unbroken insulation may be of anydesired length and may extend upwardly so that the insulation terminatesat a point above the level of the water to prevent any possibility ofleakage.

In Fig. 2 the lead wire and plug assembly-0f Fig. 1 is shown assembledwith an explosion initiator shell 9 having, an explosive compositiontherein generally indicated by III. in this modification may be formedof conventional gilding metal.

Prior to assembly of the lead wire and plug with the shell 9, theexplosive composition is charged into the shell. The lateral surface ofthe plug I is moistened with a suitable solvent for the thermoplasticmaterial of the plug and the solvent softens and tends to dissolve thelateral surface of the plug. The lead wire and plug assembly is thenforced into the upper end of the charged.

The shell 9 I55 shell 9 to close the same and the lateral surface of theplug contacts the inner walls of the upper end of shell 9, forming thejuncture generally indicated by I I.

Where the shell 9 is formed of gliding metal, the softened surface ofplug I forms an adhesive which sets upon evaporation of the solvent toform a water.tight joint.

' In the preferred embodiment of the invention as disclosed by Fig. -3,the shell 9 is made of a thermoplastic material which is compatible withthe thermoplastic material of the plug I. In assembling this embodimentthe solvent employed to moisten the lateral surface of the plug is asolvent for the thermoplastic material of shell 9 as well as a solventfor the thermoplastic of plug I. When the plug I. with itssolvent-softened outer surface is forced into the upper end of shell 9',the solvent tends to soften the surface of shell 9' adjacent thejuncture indicated at II and upon subsequent evaporation of the solventthe thermoplastic material of shell 9 adjacent said juncture and thethermoplastic material of plug I adjacent said juncture are mergedtogether.

This, in effect, forms a unitary thermoplastic housing comprising theshell, the plug, and the thermoplastic insulating material.

Solvents which may be employed in assembling the thermoplastic insulatedlead wires with the plug or in assembling the thermoplastic insulatedlead wires and plug assembly with a shell may be any suitable solventfor the thermoplastic materials to be softened therewith. In general,solvents such'as aliphatic esters, aromatic hydrocarbons and ketones maybe employed. We have found, however, that benzene or acetone areparticularly suitable.

In the assembly of the present invention, any commercially availablethermoplastic resins may be used which are compatible and which arewater-tight and chemically and electrically inert. We have foundsuchmaterials as ethyl cellulose, cellulose acetate, "Lucite (methylmethacrylate). and polyesters of vinyl alcohol well suited for the plugand shell elements of the device. Materials suitably plasticized, suchas ethyl cellulose, modi-.

fled vinyl halide polymers, and polyesters of vinyl alcohol are wellsuited for coating the lead wires.

Of these materials, we have found that the commercially available resinssuch as resins formed by the co-polymerization of vinyl chlorideandvinyl acetate are hi hly preferred. In addition to high tensilestrength, good dielectric properties and excellent resistance tochemical action and water absorption, these vinyl resins have slighttendency toward cold-flow. This latter property is of particularadvantage inthe construction of detonator assemblies of the presentinvention for the reason that the plugs, after insertion into the shell,are frequently under pressure due to the confinement of the surroundingshell and unless the material of the plug has substantial resistancetoward cold-flow it may tend to loosen in the shell.

While in Figs. 1, 2 and 3 I have disclosed, as a preferred embodiment ofmy invention, a structure in which the plug element is externallytapered, obviously. a plug of cylindrical or other form may be employed.In such a construction,

care must be taken to insure snugness of fit of plug and shell surfacessuch that moisture may not gain access to the contained detonatorcomposition. Shells of the type with which the present invention isconcerned, commonly have a slight flare at their open ends. Wherecylindrical plugs are employed, this slight flare scrvw to iacilitateinsertion of a plug of such size as to provide a forced fit with theshell proper.

In Figs. 2 and 3 we have indicated the explosive charge id as a singlecharge, it is to be understood that this may comprise a plurality 'ofcharges with or without capsules, delay fuses and the like. The ignitionelement 5 has been indicated diagrammatically as a bridge wire but it isto be understood that an electric match or other ignition element may besubstituted there-' for.

Other modifications will readily occur to those skilled in the art.

c Having fully described our invention what we claim is as follows:

The method of making lead wire and plug assemblies which comprisesboring a plug oi thermoplastic material to provide said plug with a boreoi slightly larger diameter than the diameter of a thermoplastic leadwire with which it is to be employed. threading said lead wire throughsaid bore until a portion or said lead wire lies below and lust adjacentthe lower portion of said bore, applying a solvent for both thethermoplastic insulating material oi the lead wire. and thethermoplastic material of the plug to said portion of said lead wirewhich lies below and just adjacent the lower portion of said bore, drathe wetted insulated lead wire upwardly into said plus, the residualsolvent retained on said thermoplastic material of said lead wiresoftening the hole-defining portions of the plug to such an extent as torender such portions semifiuid and sealingly adhesive with respect tothe material coating the lead wires, and merging the contiguous surfacesof said bore and lead wire insulation by dispersing the solvent.

